Parallel Fourier ptychographic microscopy reconstruction method based on FPGA.

Fourier ptychographic microscopy (FPM) can bypass the limitation of spatial bandwidth product to get images with large field-of-view and high resolution. The complicated sequential iterative calculation in the FPM reconstruction process reduces the reconstruction efficiency of the FPM. Therefore, we propose a parallel FPM reconstruction method based on field programmable gate array (FPGA) to accelerate the FPM reconstruction process. Using this method, multiple sub-regions in the Fourier domain can be computed in parallel and we customize a dedicated high-performance computational architecture for this approach. We deploy 4 FPM reconstruct computing architectures with a parallelism of 4 in a FPGA to compute the FPM reconstruction process, achieving the speed nearly 180 times faster than traditional methods. The proposed method provides a new perspective of parallel computing for FPM reconstruction.

High-performance heterogeneous FPGA data-flow architecture for Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM) is a recently developed computational imaging technique that can achieve both high-resolution and a wide field-of-view via a sequence of low-resolution images. FPM is a complex iterative process, and it is difficult to meet the needs of rapid reconstruction imaging with the conventional FPM deployed on general purpose processors. In this paper, we propose a high-performance heterogeneous field-programmable gate array (FPGA) architecture based on the principle of full pipeline and the data-flow structure for the iterative reconstruction procedure of FPM. By optimizing the architecture network at gate-level logic circuits, the running time of the FPGA-based FPM reconstruction procedure is nearly 20 times faster than conventional methods. Our proposed architecture can be used to develop FPM imaging equipment that meets resource and performance requirements.

Two-photon absorption and non-resonant electronic nonlinearities of layered semiconductor TlGaS2.

The ultrafast nonlinear optical properties of bulk TlGaS2 crystal, a semiconductor with a layered structure, are studied by combining intensity dependent transmission, time-resolved transient absorption, and optical Kerr effect coupled to optical heterodyne detection. TlGaS2 demonstrates obvious two-photon absorption and electronic nonlinearities at 800 nm. The two-photon absorption coefficient and the nonlinear refractive index are determined to be of the order of 10-10 cm/W and 10-14 cm2/W, respectively. Furthermore, both the real and imaginary parts of the complex third-order susceptibility tensor elements are extracted. The large ultrafast optical nonlinearities make TlGaS2 a promising material for application in photonic techniques.

Extended-field coverage hyperspectral camera based on a single-pixel technique.

A spectral single-pixel imaging system facilitates effective image compression, but the imaging region is limited by its single detector. This paper presents a hyperspectral camera that allows extended-field coverage to be collected by one detector. Compressive data of a large field of view is achieved by our highly sensitive detection camera, which can be extended to near-infrared or infrared spectral monitoring. We acquire a hyperspectral datacube of 256×256 spatial pixels and 3 nm spectral resolution at a sampling rate of 25%. Finally, we apply our camera to monitoring fruit freshness nondestructively by differentiating a banana's ripeness over time.

Dither removing Fourier ptychographic microscope based on a two-axis rotation stage.

SIGNIFICANCE: Large space-bandwidth product is highly desirable in many biomedical imaging. Fourier ptychographic microscopy (FPM) is a computational imaging technique that can significantly increase the space-bandwidth product of a standard microscope. The illuminator of a Fourier ptychographic microscope is not flexible at present, and it is inconvenient to meet different imaging needs. AIM: An illuminator based on a two-axis motorized rotation stage was presented to provide a more flexible illuminating way with the goal of meeting different imaging needs. APPROACH: The illuminator adopts a concentric illuminating method to provide coherent illumination in any direction on the sample plane. The sampling pattern can be freely designed and changed according to the parameters of the imaging system. A dither removing algorithm was proposed to remove the potential dither influence introduced in the image acquisition process. RESULTS: The illuminator could be conveniently integrated into different imaging systems. The feasibility and flexibility were demonstrated by applying it to imaging systems with numerical aperture of 0.045 and 0.01. The resolution gain is about 4- and 13-fold, respectively. The effectiveness of the dither removing algorithm was validated in both simulation and experiment. CONCLUSIONS: A more flexible illuminator for FPM was presented to meet different imaging needs. A dither removing algorithm was proposed to remove dither influence.

Hyperspectral imaging using the single-pixel Fourier transform technique.

Hyperspectral imaging technology is playing an increasingly important role in the fields of food analysis, medicine and biotechnology. To improve the speed of operation and increase the light throughput in a compact equipment structure, a Fourier transform hyperspectral imaging system based on a single-pixel technique is proposed in this study. Compared with current imaging spectrometry approaches, the proposed system has a wider spectral range (400-1100 nm), a better spectral resolution (1 nm) and requires fewer measurement data (a sample rate of 6.25%). The performance of this system was verified by its application to the non-destructive testing of potatoes.